The widespread use of heat exchangers in the automotive industry, coupled with the continuing need to provide lighter and more efficient devices, has occasioned the development of a multiplicity of new designs and configurations in the manufacture of condensers for use in automotive refrigeration systems.
Early heat exchangers, still in widespread use as condensers in automotive refrigeration systems, typically comprise a continuous serpentine configured tube through which gaseous and/or liquid fluids can flow. Plates or fins, introduced in contact with the serpentine tube, provide increased energy exchange surface areas. A cooling medium, such as ambient air, is passed over the tube and plates or fins thus allowing energy exchange from the warmer fluid in the tube to the cooling medium. To allow convenient assembly, the continuous tubes are manufactured from multiple "U" shaped elements to allow insertion through the fins and after assembly the elements are joined together by "U" tube connectors to form the continuous serpentine tube. In recent years, improved systems comprise parallel, spaced header tank structures interconnected with multiple parallel energy exchange tubes to allow flow of fluid, e.g. gaseous and/or liquid, between the header tanks. The multiple tubes are typically rounded or rectangular in configuration and have plate or convoluted fins disposed across or between the tubes to increase the heat exchange efficiency of the energy exchange tubes. The device is typically formed by inserting the multiple tubes into holes in the header tanks, placing convoluted fins between the tubes, welding or brazing the tubes to the header tanks and the fins to the tubes.
In the operation of a typical condenser, refrigerant gas flows through the energy exchange tubes and is cooled or condensed substantially to a liquid by a cooling air stream flowing over the tubes. The direction of the refrigerant flow stream and the cooling air flow stream are generally perpendicular to one another. The dimension along the length of one edge of the tube perpendicular to the air stream is the leading edge contacting the flow air stream and the width of this leading edge is generally referred to as the transverse dimension of the energy exchange tube. The transverse dimension of a tube is thus the average width of the tube. Therefore, a rounded tube has a traverse dimension equal to its diameter and a rectangular tube one equal to the width of its leading edge surface.
There has been a recognition that the rounded type energy exchange tube may lack the efficiencies needed for many modern automotive applications. In particular, the width of the leading edge acts as an obstruction to the air stream and it is generally desirable to minimize this obstruction. Though the rounded configuration is particularly suitable to resist the high internal fluid pressures of the automotive condenser systems, significant manufacturing assembly problems have been encountered in forming automotive condensers from small, less than 0.20 inches, rounded exchange tubes. Thus the smallest round tubes typically commercially used are larger than about 0.20 inches in diameter creating a manufacturing barrier to the formation of traverse dimensions less than about 0.2 inches.
To further reduce the width of the leading edge, e.g. reduce the transverse dimension, substantially rectangular energy exchange tubes have been proposed and are finding a degree of acceptance in the industry along with various modified rectangular configurations. Such configurations allow a smaller traverse dimension than round tubes, however, it is desirable to still further minimize air flow obstruction for the overall efficiency of the condenser.
U.S. Pat. No. 4,615,385, though particularly concerned with header tank construction, discloses a typical modified rectangular configured energy exchange tube with a plurality of tubes connected in parallel between header tanks. Therein, the tube is disclosed as being flattened such that the smallest dimension of the rectangle comprises a rounded surface which is arranged in the device to comprise the traverse dimension.
U.S. Pat. No. 4,688,311 discloses a process to manufacture a modified rectangular configured energy exchange tube which can be effective in resisting the high internal fluid pressures of automotive refrigeration systems. Therein a rectangular tube comprising the rounded configuration at the traverse dimension of U.S. No. 4,615,385, is internally fitted with an undulating fin insert which is joined with the interior of the tube throughout its longitudinal length. The internal fins act as tension struts to help withstand internal fluid pressures. Such tube requires the use of added materials in construction and is difficult to fabricate because of the difficulties of fin insertion into the tube.
It is an object of this invention to provide energy exchange structures having efficient air flow resistance at their transverse dimension.
It is a further object of the invention to provide energy exchange structures having resistance to internal fluid pressures.
It is another object of the invention to provide an automotive condenser having resistance to internal fluid pressures.
It is still another object of the invention to provide a method of manufacturing an energy exchange structure having efficient air flow resistance and resistance to internal fluid pressures.
These and other objects of the invention are achieved by the invention described as follows: